Shaft Steel Material Selection

Your professional advice as to the type of steel to use in replacing the damaged one that has been galled by Torrington needle roller beating due to the lack of insufficient lubrication.

I am considering Drill; rod oil quenched with a finish ground tolerance of 0.0005" +\- tolerance ( G.B Silver steel).

All input is much appreciated, thanks Doug in Canada.

Once the keyways have been cut in Silver Steel, it could be hardened, accepting a risk of distortion.

Although, unless the loads are great, you might well getaway with it unhardened, with new needle rollers, as long as the lubrication is good.

Howard

Silver steel(drill rod) may be ok if unhardened but by nature is a brittle steel. If lubrication is good I would try EN16T or EN19T in as supplied state. You should be able to get an equivalent specification steel in Canada.

What ever steel you use if you leave it soft after finish machining your spindle will generally not distort, if you heat treat it there will be all sorts of distortions. You state 'Drill; rod oil quenched with a finish ground tolerance of 0.0005" +\- tolerance ( G.B Silver steel).' That is before heat treat, after heat treatment it is bound to bend & scale,silver steel also tends to 'grow' in diameter so not good for your particular purpose

Tony

From Machine Design Magazine: Surface hardness 58C, 16minRa finish.

Rough machine leaving grins stock. Harden. Grind between centers. Touch up keyseats using a carbide end mill.

Alternative: If 60 case rod is available in the right diameter use it and mill the keyseats with carbide.

Here is the source of my recommendation:

**LINK**

Is the original shaft hardened? Rollers on a soft shaft will always eventually gall like that. If planning to leaving it soft then drill rod might work ok. But if you through harden and temper it, could be a bit brittle for a shaft if highly loaded. Original may have been case hardened.

Bit more info on the application, rpm, loading, hp etc would be helpful. If low rpm low load such as countershaft on a bench lathe etc you could consider using oilite sintered bronze bushings on a common bright mild steel shaft as used on Myfords etc.

Grease lubrication via that zerk fitting is not so good for needle rollers. They do better with oil.

Edited By Hopper on 27/06/2020 02:25:11

Mr Reese thanks very much for the Link , it certainly cleared up the issues I was thinking of and top information added to my education.

The idler pulley arrangement is part of a clutching system driven by a 15 Hp 4 cycle engine , I would expect top RPM to be 1,725 but most of the time it operates 2/3 to 3/4 speed in outdoor environment open field and the only practical method of lubrication is threw a grease zerk an oil;pot would collect much contaminants tho I do like the idea , mounting may curate some issues ?.

The drill rod I mentioned earlier comes from the supplier oil quenched and ground no spec as to the BHN or RH, I would only be machining to length and cutting key way slots, I am a little concerned about the as supplied ground finish that the Torrington needle bearings will be running on and should I polish the contact area. ?.

I do have a length of 3/4 ground shafting that is ment for sintered bronze bearings application, maybe I should try it?

Might it be possible to redesign the arrangement using readily available inner races? No problems with hardness, surface finish and distortion. You might even be able to use the existing shaft, if not a new shaft could be made from (relatively) easy to machine steel.

Looks like the casting could accommodate slightly larger outer races. Is that an oil seal in the photo, if not consider fitting, the "needle roller" type (slim section) would be perfect for the job.

John

Well if you can buy the drill rod already hardened and ground, that should do the job. All you have to do is figure out cutting the keyways. If its not too hard a surface maybe a carbide cutter. Or ceramic if harder. Otherwise its a grinder job.

Doug,

How many hours of running life do you need? The cost and effort of heat treating might be more than the cost of the steel and Torrington bearings. If you can cut your own keyway (of have a pal who can) might it not be better to just to make two shafts out of EN16T (as already suggested) and buy two sets of bearings? Secure the heavily greased spare shaft and bearings to the machine. According to Murphy's law, you will never ever need the second shaft!

John

John MC beat me to it, use 0.5" id 0,75 OD inner races:

https://www.bearingboys.co.uk/?catid=3665&display=&orderby=&att1=&att2=3%2F4inch&att3=&att4=&att5=

on a 0.5" shaft with 0.5" x 0.75" taper sleeve bushes on the pullerys e.g.

https://www.sdp-si.com/PDFS/Shaftloc-Sleeves-Inch.pdf

Loctite will hold the sleeves (ot turn down a 0.75" shaft to 0.5" at the ends) and you willl have room for proper seals so a semi-liquid geease e.g. CV joint grease can be used..

Robert G8RPI.